Recently, multi-pin thin-layer mount packages are used to comply with electronic devices of high integration density. Needed for such multi-pin structures is a technique for forming bump electrodes with a height of 10 to 100 μm or more as connecting terminals. When electrodes are formed by the plating method, chemically amplified positive photoresist materials are often used because a high sensitivity and high resolution can be achieved in a relatively simple way, and the photoresist film can be readily stripped after plating. When a film of photoresist material is formed, in most cases, spin coating is used to coat the photoresist material onto a substrate. Under certain coating conditions, an excess of the photoresist material is dried, before suction into the drain of the coater cup, to form floss known as “cotton candy” that floats above the coater cup, causing contamination to the surrounding and substrate.
To avoid such a phenomenon, another means of film formation is desirable. As the rewiring material used in the later step of the semiconductor manufacturing process, for example, a dry film of negative resist composition comprising a polymer of silicone structure is used as disclosed in Patent Document 1. Nevertheless, regarding the chemically amplified positive resist composition based on a phenol-containing resin as an effective component, only limited examples are found in Patent Documents 2 and 3. Specifically, Patent Document 2 refers to a limitative composition comprising a heat-polymerizable compound and a heat-polymerization initiator. In Patent Document 3, a thermoplastic resin layer must be formed as an intermediate layer between a chemically amplified positive resist dry film layer and a support film. The dry film layer has a thickness in the range of 0.5 to 10 μm. Thus the material finds only limited applications.
This is partly because polymers used in chemically amplified positive resist compositions are generally phenol-containing resins, specifically polymers having monomeric units of p-hydroxystyrene. Since polymers having a high content of phenol units are hard and brittle, films thereof are less flexible, suffering from the problem of cracking. To avoid cracking, Patent Documents 2 and 3 use a heat-polymerizable compound having two or more ethylenically unsaturated bonds in the molecule or a thermoplastic resin layer to impart flexibility. With these materials, however, limits are imposed on the characteristics that the material should exhibit in itself.
It has long been waited to have a chemically amplified positive resist dry film which is based on a combination of essential components: (1) a polymer which turns soluble in alkaline aqueous solution under the action of acid and (2) a photoacid generator capable of generating an acid in response to radiation or actinic light and contains optional additives, as in conventional liquid chemically amplified positive resist compositions, because the dry film can find a wide variety of use without limitation.